The invention relates to a method for pre-filtering training sequences in a radio communication system, in which an antenna system comprising a number of antenna elements is used on the transmit side at least.
In the case of radio communication systems, such as mobile radio communication systems, to increase data transmission capacity, antenna systems each comprising a number of antenna elements are used on both the transmit side and the receive side. Such radio communication systems are referred to as so-called Multiple Input Multiple Output or MIMO radio communication systems.
Special signal processing algorithms are used to split a digital input data stream into data sub-streams and emit them via the transmit-side antenna elements. Spatial radio channel coefficients can be derived based on the spatial arrangement of the antenna elements, representing characteristics of radio transmission channels. The radio channel coefficients for example describe signal fading, specific propagation, attenuation, interference, etc. in the radio transmission channel.
The radio channel coefficients are used for example on the transmit side to pre-filter the data sub-streams, to adjust these in an optimum manner to the radio transmission with respect to a higher data throughput or with respect to a higher level of transmission quality. For example pre-filtering brings about an individual transmit power adjustment and/or an individual modulation for every data sub-stream.
In the case of a MIMO radio communication system, radio channel coefficient determination with the aid of channel estimation is very complex. With a number MTX of transmit antennae and a number MRX of receive antennae, a total of MRX×MTX radio channel coefficients to be estimated therefore results for MRX×MTX radio transmission channels. Specifically, for a MIMO radio communication system with four transmit and four receive antennae, a total of 16 radio transmission channels results described by 16 radio channel coefficients.
In the case of an FDD (Frequency Division Duplex) radio communication system in particular, precise estimation of the radio channel coefficients requires long training sequences, which in turn take up a considerable number of radio transmission resources.
Transmitter-side pre-filtering of symbols to be sent is known from “Performance Analysis of MIMO Maximum Likelihood Receivers with Channel Correlation, Colored Gaussian Noise, and Linear Prefiltering”, Mario Kiessling et al., ICC 2003, IEEE International Conference on Communications, vol. 5, 11.05.2003-15.05.2003, pages 3026 to 3030, XP002270467, USA. The described pre-filtering allows improved receipt of the symbols to be achieved in respect of the bit error rate BER and in respect of the signal to noise ratio SNR, with pre-filtering taking place on the basis of statistical algorithms.
Transmit-side pre-filtering is known from “Statistical Prefiltering for MIMO Systems with Linear Receivers in the Presence of Transmit Correlation” Kiessling, 57th IEEE Semi-annual Vehicular Technology Conference, VTC 2003, Jeju, South Korea, vol. 1, 22.04.2003-25.04.2003, pages 267-271, XP002270468, for the dimensioning of which there is no need for a precise knowledge of channel state information CSI.
Pre-filtering is carried out based on statistical values.
Further pre-filtering based on statistical values is known from “Statistical Prefiltering for MMSE and ML Receivers with Correlated MIMO Channels”, Kiessling, WCNC 2003, IEEE Wireless Communications and Networking Conference Record, New Orleans, La., USA, 16-20.03.2003, vol. 2, pages 919-924, XP002270469.